Method of coating a crucible with sodium chloride



United States Patent 2 Claims ABSTRACT OF THE DISCLOSURE A method of coating the interior surface of tubular structures by disposing within the structure a mixture of a coating composition in a volatilizable vehicle. The mixture is confined within the structure and the structure is rotated and heated to volatilize the vehicle and deposit a uniform and continuous coating on the interior surface of the structure.

This invention relates to a process of coating the interior surfaces of tubular sections. More particularly, the invention relates to a method of coating generally cylindrical vessels, such as crucibles or the like, in a manner which provides a uniform and continuous coating on the interior surface thereof. The terms tube and tubular are used in the specification and claims in the broadest sense to refer to any hollow structure without regard to cross-sectional configuration.

It is known that the application of a coating to the interior surface of a crucible, mold or the like can be beneficial in improving the surface of metal cast therein. Many methods may be employed to provide such a coating on the interior surface. Such coatings have been applied by brushing on a mixture containing material with which it is desired to coat the surface. However, brushing may be discontinuous and also result in nonuniform coating thickness. More exotic methods which insure more uniform coating thicknesses and more general coverage of the surface may be employed but are generally expensive and economically disadvantageous. The present invention involves a simple, effective and economical method of providing a coating on the interior surface of structures and vessels used, for example, to contain molten metal.

According to the invention, there is provided a process of coating the interior surface of a tubular structure which comprises placing a mixture of a coating material and a volatile vehicle within the structure and confining same therein as, for example, by providing barriers at the ends of the structure to contain said coating mixture within the interior of the structure, rotating the sructure while heating to volatilize the vehicle and depositing the coating substantially uniformly on the interior surface of the structure.

A particular application of the above described method in accordance with the invention relates to the use of crucibles used to contain molten titanium. It has been discovered that when coatings of particular compositions are applied to the interiors of such crucibles, the ingots produced by solidification of metal therein possess a superior surface and the quality of the ingot surface shows considerable improvement over ingot surfaces produced by standard methods employing crucibles without a uniform coating on the metal-contacting surface thereof.

3,531,318 Patented Sept. 29, 1970 In the case of coating crucibles for use in containing molten titanium in accordance with one embodiment of the invention, a cylindrical crucible to be coated is placed with its longitudinal axis in a substantially horizontal position. The mixture of the coating material to be used and an appropriate volatilizable vehicle is placed in the crucible. The ends of the crucible are sealed so that the mixture will not leak out. However, vent holes may be provided in the end closures for the emission of the volatilized vehicle. The crucible is then rotated about its longitudinal axis by any appropriate means such as with the use of a belt and rotating shaft. Heat is applied along the length of the crucible and the vehicle is volatilized from the mixture. The coating material adheres to the walls of the crucible providing a uniform coating over the length of the interior surface.

The following examples will further illustrate the practice of the invention:

A mixture of 250 grams of sodium chloride salt and 10 ml. of a wetting agent with 600 ml. of water is placed in an 8-inch diameter crucible provided with vented end closures and which is secured in a rotisserie-like apparatus. The crucible is rotated and heated by a flame along its entire length. The Water in the mixture, upon sufficient heating, vaporizes into steam which escapes through vent holes in the end plate. As the Water evaporates, the salt in the solution attaches itself to the interior wall of the crucible which it contacts during rotation of the crucible. When all the water is vaporized, the salt is deposited as a tightly adherent and smooth coating on the interior wall of the crucible.

In another example, a l2-p0und mixture of sodium chloride salt with 3 gallons of water and a quantity of a wetting agent is placed in a 30-inch diameter crucible as in the previous example. The crucible is then placed on a set of carrier rolls which rotate the crucible over a gas flame placed lengthwise under the crucible. After sufiicient heating, the water in the coating mixture is driven off as steam which escapes through vent holes in the end plates of the crucible. Upon complete evaporation, the salt appears as a uniform, tightly adherent coating on the interior surface of the crucible.

We claim:

1. A method of preparing a crucible to receive molten titanium, said method comprising introducing to the crucible a solution of sodium chloride in water, rotating the crucible on its longitudinal axis while confining the solution to the interior thereof, and heating the rotating crucible to evaporate the water to dryness and deposit a tightly adherent smooth coating of sodium chloride on the interior surface of the crucible.

2. A method as defined in claim 1 in which a Wetting agent is incorporated in said solution.

References Cited UNITED STATES PATENTS 1,676,815 7/1928 Beatty 117-97 X 2,182,227 12/1939 Goldman 11797 2,623,809 12/ 1952 Myers. 3,035,318 5/1962 Campbell 117--l69 X 3,056,692 10/1962 Kitada l17--97 X RALPH S. KENDALL, Primary Examiner U.S. Cl. X.R. 

